Kids are so different but here are ones my boys have enjoyed around that age:
Books by Beverly Cleary (Ralph S. Mouse series and the Henry and Ribsy series especially).
The Boxcar Children
The Hardy Boys (the old ones, not newer ones).
The Incorrigible Children of Ashton Place series
The Mysterious Benedict Society series (these are long so a read aloud or an audio book)
Rascal
My Side of the Mountain
the Narnia series by CS Lewis
Mrs. Frisby and the Rats of NIMH